The present disclosure relates generally to electronic communications systems and, more particularly, to a quadrature modulator balancing system.
Quadrature modulators, IQ mixers, or SSB mixers are a flexible and convenient way to impart modulation onto a carrier. One of the issues with Quad Modulators is the fact that the image and carrier leak-through is a function of how well the I and Q paths of the signal are matched in phase and amplitude.
One existing technique uses a calibration approach to solve this problem. The output of the IQ modulator is monitored on a spectrum analyzer as the various coefficients are altered to get the best performance in terms of image and carrier rejection. An algorithm is used to arrive at the best set of correction factors at every transmit frequency and temperature desired. Other approaches require much more hardware to sample the output of the quad modulator and use various algorithms to arrive at correction factors. The main problem in balancing a quad modulator is determining the phase and amplitude differences between the I and Q paths.